Turns All Year Trip Reports(1) Viewing these pages constitutes your acceptance of the Terms of Use.(2) Disclaimer: the accuracy of information here is unknown, use at your own risk.(3) Trip Report monthly boards: only actual trip report starts a new thread.(4) Keep it civil and constructive - that is the norm here.

Put me in the camp that would have (and did) choose avalanche safe terrain on that weekend. I chose forested terrain and picked a destination where much of the trail breaking would be in the woods where it is easier. I would have made the same decision regardless of whether there was a persistent weak layer or not, just based on the amount of new snow in the preceding ten days. I made that decision knowing that if I made a mistake in evaluating stability and triggerred (or got caught by) a slide it could be injurious or fatal. A situation like this one is like playing with a loaded deck, one may only get one mistake.

I won't question the OP's choice of terrain. As the OP suggested, I will ask a question. The OP said that "while not completely ruling out the persistent slab". What was the Op's tolerance for risk before the incident? And how has it changed after this lucky brush with death? I think a lot of backcountry skiers would have trouble defining in real terms their tolerance for risk and how they factor into it the possibility of severe injury or death. I can say that one avalanche accident I had made me completely re-evaluate my tolerance for risk and my methodology.

I will also ask the OP if he had been following the avalanche forecasts regularly (on a daily basis) prior to planning this trip. I would note that the persistent weak layer and failures in this layer were noted nearly daily from first snowfall that buried the weak layer through about Wednesday (Thursday's avalanche forecast) before the accident (3 days previous to the accident).

I don't respect the OP's criticism of NWAC and the avalanche forecasts. Telemetry shows that only about 6" of new snow fell on Thursday and Friday at Snoqualmie Pass and therein lies the reason the OP found good stability in surface new snow layers. However, near ridge lines sustained winds in the 20's from the West with gusts to 30 also occurred through Friday. So, the OP would probably have found still unstable wind slabs at higher elevations and near ridge lines. And any avalanches could have stepped down into still recent deeper buried weak layers. In fact if the OP's avalanche was triggered by a smaller avalanche or cornice off Chair Peak the wind probably played a roll (otherwise we have to assume the massive slab was human triggered (which seems unlikely).

Having asked two of NWAC's forecasters what Considerable means to them, it means that they would expect to hear of a few incidents. That would be across the range of their forecasting area. So, the Op's finding stable surface snow where the OP travelled is really meaningless in the bigger picture. In any case the OP probably observed a small avalanche or a cornice fall of unknown size on this particular day which triggered a larger avalanche. It is evident the OP's observation of stability in this one location can only be taken with a grain of salt.

It seems we all agree that there's a persistent weak layer (or whatever you prefer to call it). When will you be comfortable to ski routes like Chair (or similar terrain) given that knowledge?

The answer is "who knows?". We'll just have to see how it plays out. I certainly won't be pushing it for a while, but there is always plenty of safe, fun skiing to be had. Since you would like some specific answers, I am going to provide some very specific answers on why specific answers are temporarily unavailable.

* The issue with persistent weak layers, and the reason that many people consider them to be unmanageable is because a persistent weak layer is an enormous engine of uncertainty relative to numerous factors that are very important for backcountry avalanche forecasting, as well as for aspects of the backcountry avalanche forecasting process itself. This is important because our perception of instability is always worst when uncertainty is highest.

- There is often a fairly basic uncertainty about the distribution of a weakness by elevation and aspect.- The duration of the drought, cold temperatures, and diurnal radiation create uncertainty about the morphology of weak crystals.- Are the characteristics of the weakness similar in most places? Different in most places? Different in a few important places?- Variations in local precipitation increase uncertainty about the depth of the weak layer from the surface.- Variations in depth from surface increase uncertainty about positive and negative changes to crystal form and interface parameters as metamorphism continues.- That is, the weakness can become worse in areas where the overlying snowpack is less than a metre deep.- Weakness can decrease in areas where the overlying snowpack is deeper than 1 metre.- Local variations in weakness vs. strength create additional uncertainty that readily propagates across various spatial scales.- On top of all this uncertainty is the normal uncertainty relative to temperature, recent load, aspect, elevation, and so forth.

Avalanche forecasting shares many characteristics with Bayesian probabilities ( prior, likelihood, posterior ) in that most predictions about current snowpack instability rely on having solid distributional information ( the winter history ) and high-quality singular information ( the current situation ).

The uncertainty inherent in persistent weak layers makes it incredibly difficult to establish both distributional and singular information, which means predictions are more akin to gambling than anything else. The uncertainty affects the information that serves as inputs to the process of backcountry avalanche forecasting, and the uncertainty affects the process of backcountry avalanche forecasting as well. I guess one could say that the uncertainty inherent to a PWL is a double whammy: not only is it harder to collect information, but the uncertainty makes it much more likely that you'll blow the prediction. These rules apply equally to EVERYONE regardless of experience, education, knowledge, hair colour, time of day, or risk acceptance level. That's why:

* Best practise dictates that decision characteristics take on an increasingly conservative flavour as uncertainty increases. Full Stop.

I don't what a guide or guides say are definitive by any means or the NWAC --there info is only a small part of my decision making of which I am ultimately responsible for...there are NO EXPERTS only people that know more than me (possibly..). Just because everybody else (who is an "expert" ) is doing something does not tell me it is safe, no matter how long they have been doing it.

If you see no sign of activity, and there are all sorts of indicators of potential danger such as a very steep slope that could be loaded (what are the indicators?)-- the steepest of slopes are obviously more prone to sliding than the lower angle ones (angle of repose...have not heard that nomenclature for years but nonetheless still applies).

Thanks for the write-up and glad you are ok--you are not alone, I too have learned the hard way.

Having said that, although the local bulletin for Whistler/Blackcomb is L/L/L it clearly notes that there is a deep persistent weak layer that has not been reacting lately but could be reactive in some isolated areas. My take on that would be that I would want to avoid the areas most likely to see that layer activated--for the moment, big, unsupported steep slopes would be completely off my list even thought the rating at all elevations is Low. A regular question is always how one will manage terrain. While the current rating locally is Low, that doesn't mean that experienced people would necessarily treat all terrain as if it were "Low" avalanche danger.

Cookie,could you simplify what you just said? We already know you are a smart guy. Insert smile face.

Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice C Hedges

Up in Whistler and noting a recent forecaster blog. Should be a great inbounds powder day tomorrow. Today there was still some breakable crust to contend with off the groomed.

Some decisions are easy. Like the choice I made this morning to have a second cup of coffee after my toddler kept me awake for half the night. Also easy was the decision I made not to wear my florescent purple jacket I still have from the early 90′s and the decision I made not to click on the link to a video of Justin Beiber being patted down in a US jail by a burly looking policeman.

On the other hand, some decisions are hard. Here’s one: where to go riding to maximize the thrill but still come back alive so you can brag about what you did to your friends at the bar. Actually, sometimes, that’s an easy one. During low avalanche hazard where you can confidently push into steep terrain, for example. During high danger, when you’re best sticking to the flats. But it’s not an easy one right now. Let me explain.

High Consequence Snowpack

We have a high-consequence snowpack right now. If you trigger an avalanche, there’s a good chance it will go big. A size 3 avalanche is big enough to destroy a car and a size 4 can pull out a 4 hectare swath of forest.

Over the last 12-14 days, a weak layer dubbed “the drought layer” has caused all kinds of problems. There have been numerous reports of large, unusual, and surprising avalanches. Some of these were remotely triggered from as far as 500 m away from where the avalanche actually ran. We had reports of avalanches running in areas with sparse trees, in small below-treeline cut blocks, and on relatively low-angled terrain. There were numerous highway closures due to avalanche activity. And tragically, three people died in avalanche incidents in Canada*.

However, in the last couple of days as I write this, the nature of the avalanche activity has started to change. We’re seeing a reduction in the number of unusual and surprising avalanches. Don’t get me wrong, avalanches are still running, both naturally (particularly on slopes that are getting hit by the sun) and human triggered (from steeper terrain and on unsupported rolls where the surface hoar was well preserved). We are also still seeing those that do run go quite large because the weak layer is deeply buried. However, we’re not getting the same kind of reports of low-angled avalanches, dramatic remote avalanches, and the super-touchiness that was characteristic of the situation this time last week.

So what we can say is, while the consequence of triggering an avalanche is still high, the likelihood of triggering one has dropped.

Since avalanche danger is a combination of the likelihood of triggering and the consequences (i.e. the size) of an avalanche, we are seeing danger ratings in many regions move into the Considerable and maybe even the Moderate range. We know from experience that when this happens many people become tempted to push out into aggressive terrain. Here’s the sixty four thousand dollar question: has the likelihood of triggering dropped enough for this to be a good decision?

Personally I don’t think so. And I’d venture most professionals would agree with me.

Boy, i'd sure love to see those reports and the data that come into nwac that the public is not privy to.like the avy incidents the commercial guys say they report to nwac. Why doesn't nwac share this data?

« Last Edit: 03/04/14, 04:47 AM by freeskiguy »

Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice C Hedges

I suspect all of this "atmospheric river" precip this week will take care of a lot of the PWL areas and might hit the reset button for most of the snowpack where I ski, Stevens to Crystal. Of course it might still be there, especially up higher, but it will certainly help alleviate my fears. PWL in Colorado don't get this kind of soaker now do they hence why they stick around for a long time during the season?

I suspect all of this "atmospheric river" precip this week will take care of a lot of the PWL areas and might hit the reset button for most of the snowpack where I ski, Stevens to Crystal. Of course it might still be there, especially up higher, but it will certainly help alleviate my fears. PWL in Colorado don't get this kind of soaker now do they hence why they stick around for a long time during the season?

Most of the reason PWL's last so long in the continental snowpack is: lack of snow, combined with cold dry weather creating a large temperature gradient in the snowpack. Meaning the air temp is much colder than the ground temp. The temperature gradient, mixed with a shallow snowpack is what preserves or even grows facets.

In a coastal snowpack like we have these layers typically don't last to long, with our warm temperatures, rain, and typically robust snowpack, although this year is a bit different.

I agree that with the warm temps, a new bridging crust layer, and the amount of new snow on to, that if the buried weak layer doesn't heal, or fail from loading, I think it will be very hard to trigger by skiing.

I've thought of going up safe routes that lead to the tops of avy terrain and dropping some big cornices, and see where we stand.

.....and were back to flaunting high risk maneuvers for interwebz adulations, hope that anyone below the cornice is as lucky as the op's party was.b

Sorry, I forgot sarcasm doesn't translate well over text. I guess I should have stayed with my original comment recommending that he "look for a cornice over a frequently traveled trail." :P

Though FWIW, dropping cornices on slopes is sometimes practiced as ghetto avy control. I would hope anybody doing this would verify the absence of anyone in harm's way. I'm not saying I endorse this, but it is done, and in fact products are sold for this particular purpose. (lawsuit inc? :P)

I suspect all of this "atmospheric river" precip this week will take care of a lot of the PWL areas and might hit the reset button for most of the snowpack where I ski, Stevens to Crystal. Of course it might still be there, especially up higher, but it will certainly help alleviate my fears. PWL in Colorado don't get this kind of soaker now do they hence why they stick around for a long time during the season?

I will also ask the OP if he had been following the avalanche forecasts regularly (on a daily basis) prior to planning this trip. I would note that the persistent weak layer and failures in this layer were noted nearly daily from first snowfall that buried the weak layer through about Wednesday (Thursday's avalanche forecast) before the accident (3 days previous to the accident).

I don't respect the OP's criticism of NWAC and the avalanche forecasts. Telemetry shows that only about 6" of new snow fell on Thursday and Friday at Snoqualmie Pass and therein lies the reason the OP found good stability in surface new snow layers. However, near ridge lines sustained winds in the 20's from the West with gusts to 30 also occurred through Friday. So, the OP would probably have found still unstable wind slabs at higher elevations and near ridge lines. And any avalanches could have stepped down into still recent deeper buried weak layers. In fact if the OP's avalanche was triggered by a smaller avalanche or cornice off Chair Peak the wind probably played a roll (otherwise we have to assume the massive slab was human triggered (which seems unlikely).

It would be interesting to fly around the Cascades (were there visibility) and see just how many and how big of slides will go between Tuesday afternoon and Thursday PM. Baker has already had 46" of new snow since Saturday and snow levels are going to 6000-7000' for the first time. I would suspect this layer will be unheard from after this cycle until about the second week of May when prolonged warm temperatures will again reawaken the monster in isolated locations.

Gary, the op has every right to offer his perception of the nwac information he reviewed. I too am critical. For example, imo, calling the folks who hide the details of client related avy incidents ''pro'' observers, just adds to promotion of a hyped hierarchy,which adds negitive bias to a safety system. Lets not confuse commercialism with professionalism.

« Last Edit: 03/04/14, 05:57 AM by freeskiguy »

Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice C Hedges

To be honest, I am a little confused by the OP's critique of NWAC. Is the claim that they were warning of too high a risk? Of too low a risk? It seems both. Granted, it is parsed between human and natural triggered, but, on the assumption that this was naturally triggered from something happening above, in the wind loading by the ridge, isn't it a fair guess that a human would have triggered a similar slide if they ventured onto the starting zone? And doesn't the "considerable" rating by definition warn of a possibility of natural slides? The Friday afternoon discussion warned of uncertainty about the deeper snow layers as well.

So I'm left a bit puzzled by the NWAC part of the OP. And left with questions such as - was the slope above the supposed "safe zone" wind loaded at any point? Were there any overhanging cornices, which given the ongoing snow movement that I noted a few miles away at mid-day on the 22nd, could have been quite fresh and unstable, and thus creating more of a risk of naturals? I don't know from the info in the report, but it seems like a reasonable guess. If the OP isn't sure or doesn't want to comment at this point, perhaps others who are familiar with that terrain might hazard a guess, given that the winds had been fairly typical in the days and hours leading up to the incident.

It would have taken an awful lot of paid observers (pro, not merely commercial) to more precisely pin down the hazard on this specific slope; and would double the number of paid observers have significantly reduced the uncertainty level about the deeper layers??

short verson- by being in terrain first after a storm i was able to see wind loading on a steep slope and avoid that area because i knew from my,not others, observations that weak snow complete with bed surface existed under two loading events. Reported x-wind load on tay aimed at specific tayer who said he was coming up in tourest mode. He reported triggering a large avy in exact spot. That area may not have appeared loaded when he skied it a day or two after the storm. Many go ski and don't wait,unless it's bad snow like heavy wet, in order to stay current with the layering. We don't always get the ''best'' lines. We are looking for the safe lines now and in the future based upon our observations. As safe lines are skied out, skiers often look for other lines in the same areas that were avoided,and that can be a trap for others who follow. To many groups skiing the same area at the same time creates a simular trap. There is a solution to these types of human traps. Care to hear it?

« Last Edit: 03/07/14, 11:44 AM by freeskiguy »

Logged

two sets of principles. They are the principles of power and privilege and the principles of truth and justice. If you pursue truth and justice it will always mean a diminution of power and privilege. If you pursue power and privilege, it will always be at the expense of truth and justice C Hedges

Thanks for stepping up when you know there will be some criticism. I don't have any criticism for what you guys did. I can only say the reasons that I chose different terrain that day and similar ones. After a few years of this sport many of us have begun to focus on what we don't know about the risks and to find ways to mitigate it more rather than to find the true barriers of what is safe or not. One rule of thumb I have fallen back to is to ski lower angled older treed terrain following a storm like this until I have more assurance that a layer like that is stable. That assurance wasn't there for me with this storm because the only dramatic change throughout the storm cycle was that more and more new snow continued to pile on top. The nwac rating, people's pits, trip reports etc. we're irrelevant too me until I saw some sort of warming or soaking event that would thoroughly test the bond on that layer. I likely would have kept to less open slopes until such an event occurred and even afterward I would have had some concern about that layer until after the first large warmup in the spring. I am not an expert and unfortunately I have not always been smart enuf to take my own advice but for what it is worth that is why I chose to stay away from terrain like chair and even the slot. I would not have posted on a trip report about chair or the slot on days with similar risks simply because I am not an expert and couldn't tell those people whether or not they made a decision that was unsafe. It is that that inability to know whether it is unsafe however that kept me in more protected terrain. Thanks again for sharing and I am glad you all came out ok. You are in good company with people who have made mistakes.

+1 This echoes my sentiments.

Also, everyone has different risk profiles - there's not one size that fits all category here. The only way to live is not go and there's no fun in that. I try to mitigate risks in every aspect of my life and the BC ranks pretty high up there...two young boys and a pretty wife will do that. Safe to all and thanks for sharing.

I've done that route and it's in a zone with no trees, lots of rollers up top, then a big wide chute. I personally wouldn't have gone near terrain like that until 2 to 3 days after the storm. The lack of snow for a long period then massive amounts of snow is a huge red flag. In avalanche training we're trained to consider the entire season of snow and the constant changing of the make-up, not just how observations a day or two before, and certainly we were not trained to rely on NWAC reports (appreciated though...).